Proton conductive polymers have been used to make membranes and membrane electrode assemblies (MEA) for fuel cells. Many addition polymers and condensation polymers have been explored as proton conductive polymers for electrode membranes. To meet the requirement of high proton conductivity at low humidity and high operating temperatures, the polymer needs to have a high ion exchange capacity (IEC). A proton conductive polymer having high IEC, however, usually becomes water soluble or significantly swellable in water. As a result, an electrolyte membrane made from the polymers typically has poor mechanical properties under fuel cell operating conditions. There is thus a need to further improve the polymer composition and electrolyte membranes to provide both high IEC and good mechanical properties.